1. Field of the Invention
The present invention pertains to a device that enables persons to detect and defeat sensors in a particular reconnaissance area in order to enable entry into such areas. The device increases the detection capability of modulated infrared light or active infrared denial devices, such as the electronic trip wires.
2. Brief Description of the Prior Art
Presently, detection personnel employ a wand-like device to detect active infrared signatures prior to entering into certain reconnaissance areas to avoid detection. Active infrared signatures are detected by optoelectronic transducers, phototransistors, that are mounted on the wand, and the wand is then placed in the fringe of the path of active infrared beams. This device has several limitations. First, depending upon the area being surveyed, it could be extremely unsafe to place the wand in a position within the direct path of active infrared beams. Second, the range of the device is not sufficient to cover a large area. Present phototransistor type devices, such as the device described above or commercially available devices used in alarm systems, etc., normally can detect active infrared signatures from up to 20 feet to 40 feet depending upon the conditions under which the device is employed. Finally, in daylight use of the detector, present configurations provide no protection from interference from the sun. Due to these limitations, a more sensitive active infrared signature detector is required in many situations.
The present invention is a device for detecting active infrared that allows personnel to detect an infrared light signature, and, therefore, avoid such signatures when entering into areas containing them. The invention comprises a photodiode detector capable of detecting infrared light, usually within a range from about 780 to about 1300 nanometers. The photodiode detector is attached to the base of a wave guide, that helps guide the infrared light to the photodiode detector. This is accomplished by incorporating a reflective surface, such as a first surface mirror, on the inner surface of the wave guide so the infrared light reflects off of the inner surface with minimal loss due to absorption. One preferred shape of the wave guide is a pyramid. An adjustable signal processing means is attached to the photodiode detector to discriminate modulated infrared light within specific modulation frequency ranges for amplification. The amplified electronic signal will indicate that active infrared is present. The amplified signal can be sent to an LED for a visual indication or a speaker for an audio indication, when the amplified frequency is within the hearing range of the operator, that active infrared light is present.
A lens, such as a Fresnel lens, can be attached to the device near the receiving end of the wave guide in order to increase the sensitivity of the device. The sensitivity of the device can also be increased by incorporating a means of adjusting the discrimination of the electronic circuit to specific modulation frequencies by means of changing the supply voltage or a negative feedback network for the amplification means within the device.
The present invention can increase the sensitivity from the normal 20 to 40 foot range of present commercially available devices to a range of up to approximately 400 feet. This greatly reduces the danger to personnel entering areas that may contain active infrared.
Accordingly, it is an object of this invention to detect active infrared from a further distance than current active infrared detection devices.
It is a further object of this invention to reduce interference from the reflection of the sun during daytime active infrared detection.
It is still a further object of this invention to reduce the hazard of placing a detection device in the direct path of an active infrared beam.
This invention accomplishes these objectives and other needs related to detecting active infrared signatures.